Subwoofer size in small room

[ThELiZ]

I’ve just built a small cinema room, measuring 5m x 3m. I’m now looking for dual subs.

When I model the room in REW, it seems that I can get away with some very small subwoofers. I’m guessing this is because the room is so small.

What I want to know is, am I missing anything by not going with larger subs, if the in room response is flat to sub 20hz with a sub that is only 35Hz -6dB?

The only thing I can think of is maybe with smaller subs, they aren’t able to pressurise the room… Or is this a myth if the sub is able to play flat under 20Hz?

Cheers

 

[NTK]

Subwoofer output is all about SPL (i.e. sound output capacity). A flat frequency response is not that important, since you'll need to measure and apply room EQ if you want optimized sound. Any loudspeaker can be "flat" down to 20 Hz*. The question is at what dB SPL.

* Note: I am sort of quoting Siegfried Linkwitz. He used 30 Hz: source

 

[sweetchaos]

^^^ 100%

Also, have you seen my subwoofer comparison spreadsheet?

It will guide you on the path to better subs.

 

[moonlight rainbow dream]

Is the room fully enclosed? You will have a much better chance of pressurizing if it's not open to any other spaces. Why aren't you factoring in a house curve? A flat in-room response especially in the subwoofer region is not satisfying at all.

Personally, if I were going to all the trouble of creating a dedicated HT, I would want subs that can go down to 20hz with their native response. And if I had no choice but to use small sealed subs that rolled off earlier than that I would definitely supplement with bass shakers to guarantee some amount of tactile feeling.

 

[ThELiZ]

Thanks all. That’s really helpful! Understood.

I completely forgot that house curves and elevated bass response is often preferable, especially for home theatre.

I will look for something that has a speaker response of 20Hz.

Was just trying to save myself some pennies, if I could.

Yes, the room is fully sealed.

 

[ozzy9832001]

Is the room fully enclosed? You will have a much better chance of pressurizing if it's not open to any other spaces. Why aren't you factoring in a house curve? A flat in-room response especially in the subwoofer region is not satisfying at all.

Personally, if I were going to all the trouble of creating a dedicated HT, I would want subs that can go down to 20hz with their native response. And if I had no choice but to use small sealed subs that rolled off earlier than that I would definitely supplement with bass shakers to guarantee some amount of tactile feeling.

This is really good advise. Flat sub region typically does not sound good. But also you have to EQ for the music you listen too. High bass can make the kick drum sound awful and give you a headache real quick.

 

[Chrispy]

Thanks all. That’s really helpful! Understood.

I completely forgot that house curves and elevated bass response is often preferable, especially for home theatre.

I will look for something that has a speaker response of 20Hz.

Was just trying to save myself some pennies, if I could.

Yes, the room is fully sealed.

Keep in mind that the spec at 20hz is often spl limited. You need to look at real 3rd party testing generally.

 

[Duke]

I’ve just built a small cinema room, measuring 5m x 3m. I’m now looking for dual subs.

When I model the room in REW, it seems that I can get away with some very small subwoofers. I’m guessing this is because the room is so small.

What I want to know is, am I missing anything by not going with larger subs, if the in room response is flat to sub 20hz with a sub that is only 35Hz -6dB?

The only thing I can think of is maybe with smaller subs, they aren’t able to pressurise the room… Or is this a myth if the sub is able to play flat under 20Hz?

Cheers

Yes boundary reinforcement will definitely extend the bass in your room, especially when the doors are closed.

I like your idea of using two small subs instead of one bigger sub. At the risk of oversimplifying:

The smaller the room, the worse the room-induced peaks and dips in the bass region. EQ can fix the peaks and (to a certain extent) the dips in a small area, often at the expense of making them worse elsewhere in the room.

One acoustic solution is to use multiple subwoofers, which you are well on your way to doing by using two subs instead of one. Two subs intelligently-distributed are about twice as smooth in-room as one sub; and four subs intelligently-distributed are about twice as smooth as two. And this improved bass smoothness tends to extend throughout the room.

In other words - and this is highly counter-intuitive! - the smaller the room, the more the in-room bass quality would benefit from a distributed multi-sub system.

Disclaimer: I have a commercial interest in a dedicated four-piece multi-sub system... BUT the technique can be implemented many different ways.

You can even use different sized subs; they do not all need to have the same low-end extension. I suggest assymetrical placement with the subs far apart. You can start with the two subs you have planned and add or one or two more later. Bonus points if you are able to elevate one sub so it's closer to the ceiling than to the floor, such that you have significant distribution of your bass sources in all three dimensions.

 

[clemenules]

Yes boundary reinforcement will definitely extend the bass in your room, especially when the doors are closed.

I like your idea of using two small subs instead of one bigger sub. At the risk of oversimplifying:

So.... at the risk oversimplifying... should he get 2 x 10" or 1 x 12" - coming from someone who's going to put subs in an even smaller room (roughly 9 x 9 ft). Not hijacking the thread as this questions still matches the thread title...

 

[ozzy9832001]

So.... at the risk oversimplifying... should he get 2 x 10" or 1 x 12" - coming from someone who's going to put subs in an even smaller room (roughly 9 x 9 ft). Not hijacking the thread as this questions still matches the thread title...

Honestly, you could go with 2x8" or 2x6". The response of the sub isn't indicative of its driver size. You will, maybe, get less distortion depending on the volume you are going to be driving them at.

I use 1x12" and 1x6" for my space which is only 11.5x9.5. They work well.

 

[DVDdoug]

it seems that I can get away with some very small subwoofers.

I'm old-school and to me 12-inches is the minimum for a woofer.

As a generalization, with a given cabinet size a smaller driver can be tuned lower. But as been said, you tend to get less SPL with a smaller driver. You aren't usually going to get bass you can feel in your body with an 8-inch woofer/subwoofer.

 

[clemenules]

I'm old-school and to me 12-inches is the minimum for a woofer.

As a generalization, with a given cabinet size a smaller driver can be tuned lower. But as been said, you tend to get less SPL with a smaller driver. You aren't usually going to get bass you can feel in your body with an 8-inch woofer/subwoofer.

I have dsp and measuring mic.

Mains are calibrated at 75db (c weighted) at mlp at -30db volume level, providing for 105db peaks. Average level in practice (music and movies) is probably closer to 65db. House curve with bass 6db above 20khz

So....
For 105 dB peaks mains =
111 dB peaks for bass (house curve)
If 2 subs, corner placement, this requires
111 dB - 6 dB corner load - 3 (?) dB double subs (conservative estimate) =
111 dB - 9 dB = 102 dB.
Room gain for my space est at 12 dB per octave from 50 dB down for sealed subs
Required output at MLP = 2.5m:
102 dB per sub at 50 hz
90 dB per sub at 20* hz
*(for argument sake let's act as if 50 > 20 is one octave down)

At 2.5m.... means

110 dB per sub at 50 hz at 1m
98 dB per sub at 20 hz at 1m
(remembering to reduce by 6db to look up cea 2010 ratings at 2m)

Which seems like quite a lot! Is my calculation correct?